1. Field of the Invention
The present invention relates to network interfacing, and more particularly to methods and systems for controlling transmission of data between network stations connected to a telephone line medium.
2. Background Art
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media
Conventional local area network architectures use a media access controller operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) protocol using a prescribed network medium, such as 10BaseT. Newer operating systems require that a network station be able to detect the presence of the network. In an Ethernet 10BaseT environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10BaseT media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based on detection of the periodic link pulses. Hence, a PHY transceiver at station A is able to detect the presence of station B, without the transmission or reception of data packets, by the reception of link pulses on the 10BaseT medium from the PHY transmitter at station B.
Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10BaseT. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air-conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak to peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmitted clock or transmit data from the received pulse becomes substantially difficult.
An additional problem encountered in European telephone systems involves the use of a network termination basic access (NTBA) device, used as an interface between the residential customer premises and a central office of the public switched telephone network for transmission of Integrated Services Digital Network (ISDN)-based signals. In particular, NTBA devices map a two wire ISDN signal from a central office into a four wire S0 bus having a two wire send path and a two wire receive path for sending and receiving the ISDN-based signals throughout a customer premises.
Another transmission scheme is the use of 2-wire UPN lines as an alternative to analog POTS lines or the S0 bus lines. UPN is a digital transmission scheme used in modern PBX systems and having the advantage of enabling intelligent digital phones to be connected to a PBX via two wires instead of the four wire S0 bus. In particular, the UPN protocol has a data rate of 384 kbps, and a 38-bit frame structure that uses AMI coding for data transmission.
Numerous problems are encountered if one attempts to supply home PNA network signals in a customer premises having two-wire UPN lines for digital telephony. In particular, the PBX systems using two wire UPN lines connect the end equipment (e.g., the digital telephones) in a star configuration. Consequently, home PNA signals transmitted from one end equipment to another end equipment would suffer substantial signal loss during transmission through the PBX, especially since the PBX is not configured for passing home PNA signals. In addition, the 384 kbps UPN signal has a number of harmonics above the 384 kHz base signal that may interfere with the home PNA signals. Further, the home PNA signal, transmitted for example at a frequency of 7.5 MHz, may interfere with the PBX equipment or the end equipment, adversely affecting reliable transmission and reception of the UPN digital signals. Finally, capacitive influences on the two wire UPN lines may adversely affect the home PNA signals, limiting the effective transmission distance between two network stations.
There is need for an arrangement for interconnecting computer end stations in a home telephone network having a private branch exchange (PBX) and configured for sending UPN-based signals on a two-wire bus.
There is also a need for arrangement for transmitting home PNA signals of a home telephone network, in a customer premises having a private branch exchange (PBX) and configured for sending UPN-based digital telephony signals on a two-wire bus, in a manner that optimizes transmission of the home PNA signal without interference with the UPN-based digital telephony signals.
These and other needs are attained by the present invention, where a customer premises system having two-wire buses for transmission of digital telephony signals between a private branch exchange and respective end equipment units includes low pass filters coupled to PBX and end equipment unit terminal ends of the two-wire buses, for isolation of a home PNA signal from the end equipment units and the PBX, and a high pass filter configured for cross coupling the home PNA signal across the two wire buses.
One aspect of the present invention provides a method of implementing a local area network in a customer premises telephone network. The customer premises telephone network has a plurality of end equipment units having respective end equipment unit terminal ends, a private branch exchange (PBX) having PBX terminal ends, and a plurality of two-wire buses. The two-wire buses are configured for connecting the end equipment unit terminal ends to the PBX terminal ends, respectively, for transmission of UPN protocol digital signals between the PBX and the end equipment units. The method includes connecting low pass filters, each configured for passing the UPN protocol digital signals and rejecting a local area network signal, at each PBX terminal end and each end equipment terminal end of a corresponding two-wire bus, each two-wire bus having a first node between the corresponding two connected low pass filters. The method also includes connecting a high pass filter, configured for passing the local area network signal and rejecting the UPN protocol digital signals, across each of the two-wire buses at the corresponding first node. The local area network signal is then transmitted from a first network node on a corresponding first of the two-wire buses at the corresponding first node.
Connection of the low pass filters at each PBX terminal end and each end equipment terminal end ensures that the PBX and the end equipment units are able to send and receive UPN protocol digital signals without interference from the local area network signal. In addition, the low pass filters limit the UPN protocol digital signals, providing a distortion-free transmission medium for the higher frequency local area network signal. Moreover, connecting the high pass filter across each of the two-wire buses at the corresponding first node enables the local area network signal to bypass the PBX without introducing crossover of the UPN protocol digital signals. Finally, the low pass filters and the high pass filter can be configured to minimize the capacitance encountered by the local area network signal on the two-wire buses, improving transmission performance and enabling the network length between two network nodes to be substantially increased
Another aspect of the present invention provides a computer network. The computer network includes a private branch exchange (PBX) having PBX terminal ends and configured for sending and receiving UPN protocol digital telephony signals, a plurality of end equipment units each having an end equipment unit terminal end and configured for sending and receiving the UPN protocol digital telephony signals, and a plurality of two-wire buses configured for connecting the end equipment unit terminal ends to the PBX terminal ends, respectively. Each two-wire bus has a first low pass filter connected at the corresponding end equipment unit terminal and a second low pass filter connected at the corresponding PBX terminal end. The first and second low pass filters are configured for passing the UPN protocol digital telephony signals and rejecting computer network signals. Each two-wire bus also has a connection node between the corresponding first and second low pass filters for a corresponding network node, where a high pass filter is configured for passing the computer network signals across the two-wire buses at the respective connection nodes.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.